PWHT 1

[tsaku100]

Hi,

Is it possible to weld a attachment in a PWHT completed vessel. If it is, guide how to do.

 

[bernoullies123]

Sure. Just weld your necessary attachment on.

 

[tsaku100]

Hi, I am not clear. What is the procedure need to be followed during new attachment in a PWHT completed vessel

 

[SnTMan]

tsaku100, while I believe there are some exceptions, most often local PWHT of the attachment weld would be required. If this is not new construction it would fall under a post-construction code, such as NBIC.

Regards,

Mike

 

[tsaku100]

In my case, its a new vessel (Done PWHT). I need to attach steam tracing support clip. It seems to be tag welded. Does that tag weld also requires local PWHT?

 

[jte]

tsaku-

Let us know if thread794-264274 does not answer your questions. If you need further info, please first let us know why the vessel is being PWHT. There may be a substantial difference if the heat treat is required for process vs required for Code reasons.

jt

 

[tsaku100]

Hi,

Let me brief my current situation. I am handling more than 80 vessels out of many Post weld heat treated vessels (Some have process reasons and some have mechanical reasons)
have the requirement of steam tracing coils.
Now vendor cannot proceed with vessel PWHT with steam tracing coils. Hence we are planned to completed PWHT first. Then complete the steam tracing.
Locating the steam tracing coil need a clip need to be welded.
Hope u understood.

 

[jamesl]

It depends on if the clip attachment welds are required to have PWHT per code or for other reasons. For carbon steel vessels, additional PWHT usually is not required for welds attaching clips that are used to support steam treacing tubing. If you have Cr-Mo materials, PWHT will be required.

All welding shall be done before hydrotest.

 

[vesselfab]

when pwht is required for thickness (ASME) you can get AI approval along with client approval to weld small welds on after PWHT as long as you follow the procedure set forth in ASME code....preheat & small weld.

When pwht is required for service, normally you write up a procedure saying preheat, WPS, Temper bead, etc and submit it to the user and let him decide

 

[rneill]

If the PWHT was for code compliance reasons then small welds can be done in compliance with code without necessarily requiring PWHT.

If the PWHT was for service reasons (e.g., sour service) then any welding following PWHT would require local PWHT, or would need to follow a strict welding procedure as described by vesselfab, and should be submitted to the end user for approval.

Most end user's have specifications that say there shall be no welding on the vessel following PWHT if the PWHT is for service reasons.

 

[jte]

For relatively thick wall vessels, small external welds may not cause problems if the PWHT is for process reasons. Welding to the "wetted surface" is altogether different.

If you have 80 vessels, you'll need to make 80 decisions.

jt

 

[AIOR]

I assume that you are dealing with a UCS material, no process PWHT necessary. Here are some Code statements:

UCS-56 (a): PWHT is required when the nominal thickness, as defined in UW-40(f), exceeds the limits in Table UCS-56. (This means that not all welds require PWHT).

UW-40 (a) (5): heating a circumferential band containing nozzles or other welded attachments that require postweld heat treatment... (see: not all attachments require PWHT).

My opinion: if your attachment fillet weld has the throat dimension less than specified in the Table UCS-56 you do not need to do PWHT for those welds. Nevertheless, I would recommend to research Code interpretations.

Another option: to avoid potential problems with a Customer just do a local PWHT of your attachments welds.

 

[bernoullies123]

why didn't you weld the clips prior to PWHT? Stress relief for process reasons is generally on the process side... but as a client I wouldn't let a lighter near my vessel after PWHT. Check with your client and play the schedule card and you'll be home free, but be careful of such playing cards as you might find your self out of business. Good luck.

 

[buick455gs]

You did not post enough information for anyone to be able to answer your question. I assume the vessel is designed and built to ASME section VIII but this is not even stated. In some cases there are exemptions to mandatory PWHT but you have to be wihtin the code requirements. In short you need to follow the requirements in the ASME code.

 

[stanweld]

tsaku100,
Assuming that the vessel is not in Lethal Service or subject to PWHT due to process service, per ASME VIII, Div. 1, UW-40 (f) "the nominal thickness is the welded joint as defined below.
(f)(3) For fillet welds, the nominal thickness is the throat dimension.
(f)(5)(f) the thickness of the weld at the point of attachment when a nonpressure part is welded to a pressure part..."

Per Table UCS-56, Note 2 "Postweld heat treatment [for P-No.1] is mandatory under the following conditions:
(a) for welded joints over 1 1/2in. (38 mm) nominal thickness.
(b) for welded joints over 1 1/4-in..."

Therefore, assuming that the throat of the fillet weld is less than 1 1/4 inch, you may make the welds without subsequent PWHT.

 

[buick455gs]

You really need to read and follow the code as there are specific requirements for vessel welds and what is stated above is only part of the answer. In general, yes can weld to a vessel that PWHT has been performed but there are limitations (i.e. total PWHT time) and conditions which have to be met. In some cases you can also perform the welding to the vessel without further PWHT but again there are process and design limitations, i.e. weld size, preheat requirements, etc.

 

[vesselfab]

ummmmm stanweld

I do not think that is a correct statement

 

[stanweld]

vesselfab,
Per UCS-56 (a)"Except as otherwise specifically prvided in the notes to Table UCS-56 and Table UCS-56.1, all welds in pressure vessels or pressure vessel parts shall be given a postweld heat treatment at a temperature not less than specifed in those Tables when the nominal thickness, as defined in UW-40(f), including corrosion allowance exceeds the limits in those Tables. The exemptions provded in Table UCS-56 or Table UCS-56.1 when postweld heat treatment is a sevice requirement as set foth in UCS-68..."

I stand by the definitions of nominal thickness as previously quoted from UW-40(f)(3)and (f)(5).

 

[vesselfab]

well, he is talking about welding on previously PWHT pressure vessels.

ucs-56 has rules set up for size of welds allowed to be welded after PWHT.

If memory serves me, it lists a small throat, maybe 3/8" if preheat is done at like 200-300*F

the rules you are speaking of is exemption from pwht, not welding after pwht.

OR maybe i misunderstood the whole basis of the original poster's statements.

 

[jte]

As I stated in thread794-264274, with a proper preheat the fillet weld throat is limited to half an inch, thus a 5/8 leg will be ok for the right materials and for Code reasons only. Still have to arm-wrestle the materials types if we're dealing with wetted surface issues and PWHT for process reasons.

jt